Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $69.88   8.294%   $75.6758   $75.68   $75.70   $75.70  
  Purchase #2 $32.43   13.497%   $36.8071   $36.81   $36.80   $36.80  
  Purchase #3 $146.55   4.325%   $152.8883   $152.89   $152.90   $152.90  
  Purchase #4 $170.40   11.141%   $189.3843   $189.38   $189.40   $189.40  
  Purchase #5 $168.26   11.854%   $188.2055   $188.21   $188.20   $188.20  
  Purchase #6 $246.74   10.184%   $271.868   $271.87   $271.85   $271.90  
  Purchase #7 $112.63   8.860%   $122.609   $122.61   $122.60   $122.60  
  7 purchase totals = $946.89       $1,037.4380   $1,037.45   $1,037.45   $1,037.50